Techniques to characterize and detect sources of ambient air contamination are described. Chemical techniques to identify indoor contaminants are outlined, they include gas chromatography, or colorimetric detection. Organics generated from indoor materials at ambient conditions and upon combustion are characterized. Piezoelectric quartz crystals are used as precision frequency determining elements in electronic oscillators

Nulton, C. P.

Silvus, H. S.

English

NASA Technical Reports Server

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AMBIENTAIR CONTAMINATION--CHARACTERIZATIONANDDETECTIONTECHNIQUES
C. P. Nulton and H. S. Silvus
Until recently,work on indoorcontaminationhas focused_rimarilyon:
,. i) the criteria air pollutants [oxides of S, N and C, p_rtic,llatesand
ozone];2) uniquely indoorcontaminants[e.g., radon, formaldel;yde,tobacco
smoke and asbestos]; and 3) the work place pollutantsfor which _erican
Conferenceof GovernmentalIndustrialHygienists (ACGIH) sets guidelines
; [e.g., organicsolvents,metal fumes and wood dust).
Currently,concerncenters on outgassingof syntheticconstructionand
,. maintenance materials such as adhesives, sealants, insulation, wall
' coverings, cleaners, and electronic equlpment inside of new, well-
)
insulated,energy-conserving buildings. The effects of outgassing of
synthetic materialsin a closed system on human health and productivityis
relevantto Space Station.
Indcorcontaminants may cause acute reactions (e.g., poisoning by
combustion products) or, more often, chronic problemsdevelop due to low-
level, long-term exposure. Southwest Research Institute (SwRI) has
assistedmany industrialclients in determiningthe sourceof contamination
of the lattertype that cause decreasedworker productivity.
Ch_ical characterizationof indoor contaminantscan be divided into
methodswhich are designedto target c_pounds, and those which provide for
a broad range search. Typical of the for_erare the National Institute of
OccupationalSafety and Health methodsthat often involveeither the use of
solid adsorbants,or liquidimpingersfor sampling followed by analysis for
( target compuunds by GC, or colorlmetrlc detection. In cases where an
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2orga,_iccontaminantis suspectedbut unknown, broader range techniques are
-equired. Samplesmay he taken by pullingambient air through adsorbants,
e.g., Tenax• and Carbosieve°, which can be desorbed thermally onto GC
columns for subsequent GC/MS analysis. A further refinement is to
cryogenically focus the trapped organics then to volatilize them as a
discrete plug onto a fused-silicacapillaryGC column, thus obtainingthe
advantagesof increasedresolutionand overall superior chromatography.I
Another approach to organicsampling is the use of polyurethane foam
C
(?UF) plugs which are relatively inert and allow for the collectionof
+_ large samplevolumes (e.g.,2S5 L/min for 4 hours). PUF samples have been
+ used to samplefor trace concen.rationsof relativelyhigh molecularweight
organics,e.g., PCBs, dioxins and pesticides.2,3
At SwRI we are characterizing the organics generated from indoor
materialsat ambientconditionsand upon combustion. These experi_nts are
conductedin a closed system (bell jar) with evolved organic compounds
being collected on Tenaxm, PUF plugs and/or liquid impingers. In one such
study organic emissions from a very small electrical fire were
characterized. A 5-cm2 postion of circuit board was placed in the test
vessel and a resistor (I00 ohm) was overloaded causing it to flare and
scorch approxlmately I cm2 of the clrcult board. The duration of the
"fire"was approximately10 seconds. The volume of the test vessel (2.B L)
was then collected on Tenax• and analyzed by GC/MS to reveala varietyof
organics (Table I) including halogenated and aromatic hydrocarbons.
Analysts of system blanks also showed that the 5-c_ portion of circuit
board emttted detectable levels of trtchloroethylene and
trlchlorotrlfluoroethaneat ambient conditions.
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An additiona] example is provided by the organicemissions from an
insulation materla] that causes dramatic biological effects when
combusted.4 Although a wide variety of organicswere characterized(Table
2), the chemical responsiblefor its unusual biological activity has not
yet been identified.
Departing from the discussion of airborne contaminant
characterization, I want to mention briefly the de:ection of critical
levels of specific compounds or compound classes with coated quartz
oscillators. Sensorsof this type may be used to prot,ct equipmentas well
z
-_ as people.
Piezoelectric quartz crystals have been used for many years as
precisionfrequency-determiningelements in electronic oscillators. When
properly cut and prepared, such crystals can maintain the frequencyof an
oscillatorstablewithin a few parts per million over a nominal temperature
range; with close temperaturecontrol, frequencystabilityon the order of
parts per billioncan be achieved.
• The resonantfrequencyof a piezoelectricquartz crystal i_ determined
by the particular mechanical mode in which the crystal operates anQ by
certain criticaldimensionscharacteristicof the mode. Additionally, as
, with any mechanical vibrating system, mass added to the surface of the
crystal producesa loading effect that lowers resonant frequency. The
absolute change in frequency is linearly related to added mass over a
s,_bstantialrange.
At SouthwestResearch Institute,this basic principlehas been applied
to measurement of the quantityof odorant in ndtural gas.5 The technique
employed is to apply a thin coatingto the surfacesof a quartz frequency-
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1985021227-170
4controlcrystal. The materials in the coatln_ were de_Ignudto react with
tertiary butyl mercapt_n (TBH), a commonly used odorant for natural gas.
The crystalwas connecteain an electronicoscillatorcircuit, oscillation
" "requency of which was monitored by a precision electronic counter.
Odorant-containing natural gas was flowed through a sample chamber
surroundlrgthe crystal (see FigureI), and oscillatorfrequencychanged in
inverse proportionto the mass added to the crystal by reaction of the !
odora,}t with the crystal coating. By using Known concentrations of
_ odorant it was possible to calibrate the frequency change in terms of
-'_ odorant concentration.
Approximately S parts per million of TBM is commonly used in natural
gas as odorant. The instrument descrlbed could readily quantify this
concentration of odorantwith a precisionof +--0.5part per million (Figure i'
2) and could detect changes in odorant concentration of less than I part
per million absolute.
Quartz oscillators have a number of advantages for alr monitoring
including their small size, inherent sensitivity _nd potential for
tailoring either coatings or the active quartz surface for high
specificity.
Althoughthe worn I have brieflydcscrlbedcharactef;zlngorganic air
• contaminants and detecting crltlcal levelsof target compoundsIn alr Is
not relateddirectlyto cabin atmospheresthe techniques involved become
increasinglyrelevantto NASA as the dur,,lon of manned flights Is extended
and the volu_eand variety of on-boardmaterialsIncr_se.
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REFERENCES
I. PeIlizzari,E. D. Developmentof AnalyticalTechniquesfor Measrring
Ambient Atmospheric Carcinogenic Vapors. EPA Contract 68-02-1228,
November 1975.
2. Lewis, R. G., A. R. Brown, M. D. Jackson. Anal. Chem.,49:1668. 1977.
3. Lewis, R. G. and M. D. Jack_on. Anal. Chem. 54:592, 1982.
4. Kaplan, H. These proceedings.
5. Millar,J. D., H. S. Silvus, L. M. Adams, H. J. Schattenberg Ill and
L. L. Altpeter. Development of a Portable I_strumentto Determine
Odorants in Gas DistributionLines. Presented at the International
Gas ResearchConference,Lnndon England,June 1983.
,I
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i98502i227-i72
TABLE I. ORGANICS ARISINGFROM FLARING A RESISTOR
"_ Class Compound , Amount2 n_
Br-containing bromomethahe 26,000
dibromomethane 3,409
bromebenzene 2,500
br_noethane <1,000
Cl-containing 1,1,1-tr!chloroethane 170,000
dichlorobenzene 78,000
trichIorott4fluoroethane 53,000
1,l-dichloroethane 22,000
1,1-dichlor_thylene 20,000
dic,.lo-otrifluoroeth_ne 6,400
chloroform. 6,400
vinyl chloride <],000
/' Aromatic Hydroc*rtJns toluene 75,000
C2-)enzenes 36,000
benzene 22,000
Aliphatichydrocarbons _ 80,000
OThers benzofuran 1,800
benzoaldehyde 1,800
phenol <I,000
acetone 5,200
methylbutync 5,200
methylbutanol 5,100
methylpentanone <I,000
2-furancarboxaldehyde <I,000
dimethylethylborane 1,000
benzonltrlle 1,000
2-propenenltrlle <k,O00
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i, ri
TABLE 2. COMPOUNDSGENERATEDBY HEATING COMMERCIALINS'JLATION
Chloromethylpropane
Oichlorobenzene
Benzene
L Toluene
Xylenes
Pyridine
Methylpyridine
MethylpropeneitriIe
" BerJzonitril e
MethylbenzonitriIes
DimethylbenzonitriIe
-,- Carbon Disulfide
•_ Methylthiophene
_ Methylisothiocyanate
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EXHAUST SEAL
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Figure 1. Experimental Arrangement for Evaluation of Quartz-Crystal
Odorant Analyzer
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90-
80-)..
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u, 70-t_
MJ
z_
:- e.,,. 60-
_ 60-
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,. _ 30-
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._ 10-
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0 1 2 3 4 5 6
PPM TBM BY GC
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Figure 2. Responseof Quartz-Crystal Sensor to KnownConcentrations '
of TertiaryButyl Mercaptan in Methane
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1985021227-176


Ambient air contamination: Characterization and detection techniques

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